The present invention relates to a process for producing a continuous web of a metallic substrate having an electric insulation layer thereon and an apparatus for the process.
Heretofore, there has been used a solar battery comprising a plurality of solar cells formed on a substrate in a pattern and connected in series, and a printed circuit board having high heat resistance and low heat conductivity has also been used.
In such a solar battery, since the cells must be connected in series, it is necessary that adjacent cells are electrically insulated. For example, when a metallic substrate is used as a substrate for a solar cell, the substrate must be subjected to insulation treatment. Usually, such treatment comprises the steps of polishing the surface of a web of a metallic substrate which is rolled out, attaching a protective sheet thereto, cutting the web in a predetermined shape by etching or by press, removing the protective sheet, and then subjecting it to insulation treatment for formation of an insulation layer. On the thus formed insulation layer a patterned back electrode is formed by vapor deposition or sputtering. The back electrode may be formed over the surface, and then patterned by etching.
In the production process described above, the cut substrates must be handled one by one, which requires much time and labor, and many handling procedures decreases the yield and productivity. As considered from the operation in the individual processing steps, usually, a batch system is suitable for the production process.
When the active layers of a solar cell are formed, the substrate must be heated to a temperature as high as 200.degree. to 350.degree. C. and hence the insulation layer is required to be resistant at such temperature. For this reason, a resin having a good heat resistance such as a polyimide is used as a material for the insulation layer. The process for forming the insulation layer of the resin comprises the steps of coating a metallic substrate with a polyimide resin by spin coating or dipping, and heating the resin coating for curing the resin and for degassing. However, this process is very complicated and entails a high reject rate. Generally, the higher the layer forming temperature in the active layers of the solar cell, the higher the quality of the solar cell. However, in case of producing a solar cell by using the substrate having the insulation layer of polyimide resin, or the like, the layer forming temperature is at most 250.degree. C. because cracks occur in the back electrode when subjecting the substrate to a higher temperature. Moreover, condensation takes place in the insulation layer of the resin during heating to emit H.sub.2 O and impurities, whereby detracting from the performance of the solar cell.
Accordingly, use of the substrate having the insulation layer of the resin is not advantagous to produce a high quality solar cell.
The field of a printed circuit board calls for development of a printed circuit board in a form of an insulated metallic substrate in view of its heat resistance in soldering and of its low heat conductivity.
An object of the present invention is to provide a process for continuously forming an insulation layer of an inorganic insulation material and a back electrode on a metallic substrate and, if necessary, cleaning the substrate, patterning the back electorde and cutting the produced insulated substrate, whereby reducing time, cost, processing steps and labor while increasing yield, productivity, and heat resistance, and further improving the performance of the solar cell itself.